Fountain pen wetness refers to how much ink the pen puts on the page and how fast it puts it there. A wet, well flowing fountain pen is desired by many users and collectors and helps in making the overall writing experience smoother and more comfortable by lubricating the nib as it moves across the paper. There are three main factors that contribute to a wet fountain pen and I'm going to go over them all. Please enjoy.
The nib of the pen plays the most important roll in your fountain pen's flow. If the distance between the tines of the nib are too narrow, ink will struggle to flow through them. If the space is too large, ink will not be able to flow with capillary action, making your pen useless. Because of this, it is important to have the perfect balance. You should be able to see a thin beam of light passing all the way through the length of the tine gap when held up to a window or lamp. This ensures that the ink has enough space to travel through. If it's a pen you feel comfortable messing with, I recommend trying to widen the nib tine gap yourself with a brass shim and see where that gets you. If it's a valuable pen, or a pen you care about, you should send it to a nibmeister to work on.
The feed contributes to pen flow by allowing ink a route to travel from the inside of the fountain pen to the tip of the nib. Although ink starvation and dryness can be caused by a thin ink channel in the feed, it is much more likely that the ink channel is blocked or the feed is not properly aligned with the nib. If the ink channel is blocked, your pen will benefit from a flushing and soaking in room temperature water. If the nib and feed can be taken out easily, (I.e. friction fit) you can try to reset them so that they are realigned. Flex pens often have very wide ink channels to help the flow keep up with the flexing of the nib. In that case, the feed is almost never the cause of a dry pen.
The last major factor of your pen's wetness is the ink. The ink you put in your pen is easy to change to improve flow. Usually, ink made by pen companies are on the dry side and flow slower than ink made by ink companies like Diamine and Noodlers. If you want a wet flowing pen, I recommend using an ink like many of the offerings by Diamine and Noodlers and if that's not wet enough, you should try a lubricated ink like the Noodlers eel series.
I hope this was helpful in making your writing experience better. If I missed anything, please let me know. Thanks for reading.